However a dev on fast hardware can still run profiles, and the fast hardware decreases the change/build/test cycle by more than enough to make it worthwhile.
The only use of a slow machine is it gives a point where you can say more optimization isn't worth it. Everything else I can do better on a fast machine than a slow machine.
It lacks one inventive. There are many incentives. Many developers love making things faster. Many developers get feedback from users which is itself incentive. Many projects track performance and that provides incentive. Many developers have a boss who cares about such things (this is the least likely of the above).
The only use of a slow machine is it gives a point where you can say more optimization isn't worth it. Everything else I can do better on a fast machine than a slow machine.